Electricity + Control 2019

PRESSURE + LEVEL MEASUREMENT + INSTRUMENTATION

Differential pressure measurement in tough conditions

Claudia Homberg, VEGA Grieshaber KG

An innovative duo of ceramic and metallic measuring cells optimises the distillation process, even under tough conditions.

Take Note! The vapour pressure of liquids plays a critical role in the production of plas- tics additives. The more precise the values, the clearer the processes and the higher the potential for plant optimisation.

1

M eeting the highest safety standards in all process steps is a critical require- ment in the chemical industry. There is a small but important element in BASF’s highly efficient safety management system at its Swiss site in Kaisten. It’s in the form of a guarantee that all processes are completely free of silicone oil. Traditional differential pressure transmitters work by means of capillary lines filled with silicone oil, which – in the unlikely event of an accident – could come into contact with the medium. In con- trast, VEGA electronic differential pressure meas- uring systems provide safety, with a combination of ceramic and metallic measuring cells. Plastics have been produced on an industrial scale for over 100 years. But anyone who spent their childhood in the 1970s or ‘80s knows that the plastics of yesteryear have little in common with today’s special plastics. The coveted toy figures quickly turned yellow and some of the Lego bricks became brittle. Plastics age as a result of thermo- oxidative degradation, that is, under the influence of heat and oxygen.The fact that plastics today can be colourfast and elastic, crystal clear, high gloss,

The eye in the storm The vapour pressure of liquids plays a decisive role in the production of such additives. Its pre- cise measurement contributes to BASF’s efficient control of special processes and provides addition- al information on how process components can be optimised and plant availability increased. The more precise the values, the clearer the process- es and the higher the potential for optimisation. In the Kaisten plant there are extreme conditions: ag- gressive substances and acids which can adhere to vessel walls forming deposits, as well as high vacuum and steam levels. Through all this, the reli- able measuring results of VEGA pressure transmit- ters are decisive. Silicone oil-free measurement While conventional differential pressure transmit- ters were previously used for level measurement, BASF’s measurement and control engineers in Kaisten decided to replace the instrumentation. They have switched process control over to elec- tronic differential pressure measurement, which is silicone oil-free, without capillary lines and there- fore without mechanical pressure diaphragms. Largely due to the ceramic measuring cell, this system is ideal for use in vacuum conditions and high temperatures. Markus Stoll, BASF’s Head of Specialist Workshops EMSR, says, “The deci- sion for electronic differential pressure measure- ment on the basis of ceramic CERTEC ® measur- ing cells was obvious, in view of their reliability in withstanding abrasive substances. Our plant is completely automated and operates 24 hours a day, seven days a week.” Stoll, together with his team, is responsible for ensuring maximum plant availability.

The combination of ceramic and metallic measuring cells best meets the challenges in the distillation reactors of the Kaisten plant.

abrasion-resistant or even heat-resistant, is due to a wide variety of specialist additives.

Plastic additives, including large-volume antioxidants and many customer-specific mixtures, are produced at BASF’s Kaisten site in Switzerland.

32 Electricity + Control

JUNE 2019